Protein synthesis Flashcards
Give an overview of protein synthesis
- 2 stages:
- Transcription
- Production of mRNA from DNA
- happens in Nucleus - Translation
- Production of polypeptides from the sequence of codons carried by mRNA
- happens in Cytoplasm on ribosomes
Describe the structure and function of mRNA
Made by transcription in the nucleus
- Acts as a template for translation in the cytoplasm
- Sequence of bases on RNA determines sequence of amino acids in polypeptide chain
- Straight chain molecule
- Triplet code = codon
- Chemically unstable
- So breaks down after a few days
Describe the structure and function of tRNA.
- Carries an amino acid
- Amino acid binding site
- Anticodon = 3 bases
- Anticodon bases complementary to mRNA codon
- Each tRNA specific to one amino acid, in relation to its anticodon
- Single polynucleotide strand
- Folded – 3 hairpin loops = three-leafed clover shape
- Held together by hydrogen bonds
Compare and contrast the structure of mRNA and tRNA.
- Similarities
- Both single polynucleotide strand
- Differences
- mRNA single helix / straight,
whereas tRNA folded into
clover shape - mRNA is a longer, variable
length, whereas tRNA is
shorter - mRNA contains no paired bases
or hydrogen bonds, whereas
tRNA has some paired bases and
hydrogen bonds
- mRNA single helix / straight,
Describe the process of transcription.
In nucleus
- DNA double helix unwound by helicase
- Hydrogen bonds broken
- RNA nucleotides align next to their complementary bases on the template strand
- Forming hydrogen bonds
- Uracil replaces thymine in RNA
- RNA polymerase joins adjacent nucleotides - condensation reaction
- Forming phosphodiester bonds
- When RNA polymerase reaches stop codon, mRNA detaches from DNA
- mRNA leaves nucleus via nuclear pore
Explain what is meant by post transcriptional modification.
Eukaryotic genes contain
- Exons – coding regions
- Introns – non-coding regions
Splicing
- Introns removed
- Exons spliced together in different combos for different proteins
Prokaryotic DNA doesn’t contain introns
- mRNA produced directly from DNA
- No splicing
Describe the process of translation.
Sequence of mRNA codons determines sequence of amino acids
- tRNAs carry specific amino acids, in relation to their anticodon
- At the ribosome, tRNA codon binds to mRNA codon
- tRNA anticodon complementary to mRNA codon
- Hydrogen bonds formed
- First codon = start codon
- Two amino acids joined by condensation, forming a peptide bond
- Using energy from ATP
- tRNA detaches (without its amino acid), ribosome moves along mRNA to next codon
- Continues until stop codon (polypeptide released)
Explain the role of ATP in translation.
-Hydrolysis of ATP, to ADP + Pi, releases energy
- For the bond between the amino acid and its corresponding
tRNA molecule
- Amino acid attaches at amino acid binding site
- For peptide bond formation between amino acids
Explain the role of tRNA in translation.
-tRNA attaches to and transports a specific amino acid, in relation to its
anticodon
- tRNA anticodon complementary base pairs to mRNA codon, forming
hydrogen bonds
- Two tRNAs bring amino acids together for the formation of a peptide bonds
- About 60 types of tRNAs to carry 20 different amino acids
- Genetic code is degenerate
Explain the role of ribosomes in translation.
Ribosome attaches to mRNA and houses tRNA, allowing codon-anticodon complementary base pairing
Allows peptide bonds to form between amino acids
How does the base sequence of nucleic acids relate to the
amino acid sequence of polypeptides?
- tRNA anticodons are complementary to mRNA codon
- E.g. mRNA codon = ACG; tRNA anticodon = UGC
- mRNA sequence of bases / codons are complementary to sequence of bases /triplets on DNA template strand
- E.g. mRNA base sequence = ACG UAG AAC; DNA base sequence =
TGC ATC TTG - In RNA, uracil replaces thymine
